Signature verification apparatus and method utilizing relative angle measurements

ABSTRACT

A signature verification system consisting of a durable pressure sensitive data input stylus, signal processing, and computer algorithms for enrollment of signatures, digits and verification. The stylus contains two transducers placed so that axial force and lateral force are measured simultaneously. Combining the two signals at digitized sample points yields a ratio of pressures indicative of the angle of the stylus to the writing surface at that moment, controlling for variations in actual force. The ratio, called a relative angle, is calculated for the entire signal train of a signature and for various simple divisions, or segments. Segments are equal divisions of the signal train by various divisions. While the relative angle of the whole signature may vary unpredictably between signings, the unique variations around the average relative angle form unique signature discriminates. Variations are measured by comparing relative angle measurements of segments, one to another, in all mathematical combinations. The combinations are called measurement points and each measurement point has a value based on the comparison. Some measurement point values, out of many sampled by computer, are uniquely consistent for particular signers. These unique measurement points and their limited ranges of variation are determined during enrollment and become the signature discriminates. These signature discriminate measurement points and values electronically distinguish an enrolled signer. The date, if enrolled, and digits for document identification, if enrolled, provide further signature verification. Verification is simplified by comparing only chosen reference measurements to determine if the incoming values fall within the acceptable range of values. An easily adjustable score determines rejection or acceptance of a signature to be verified. The stylus itself is continuously calibrated by adjusting a measurement step, not the transducers themselves.

BACKGROUND OF THE INVENTION

This is a continuation-in-part patent application of application Ser.No. 08/418,835 filed on Apr. 7, 1995 of Michael E. Lee entitledSIGNATURE VERIFICATION APPARATUS AND METHOD UTILIZING RELATIVE ANGLEMEASUREMENTS, now abandoned.

BACKGROUND Description of Prior Art

For many years significant efforts have been made to develop systemsthat reliably establish the identity of a person. More recently, systemshave attempted to link that identity verification to the verification ofthe date and to the verification and authentication of the content of amessage generated or transmitted electronically. Such systems are deemeddesirable from the point of view of both the identifier and theidentified in a variety of settings. Some uses for identify verificationsystems include: credit card transactions, access to computer programsand information, electronic funds transfer, and the electronictransmission of legal documents and signatures. In these types ofsituations identity verification must be inexpensive, reliable, andnon-intrusive.

Many proposed systems measure some biological trait unique to theindividual. Reference measurements are taken and stored for comparisonlater at the time of verification. For example, there exist systemsusing voice recognition, palm print recognition, and laser retinalscans. These systems have achieved some success in terms of reliabilityand utility in restricted situations. Retinal scanners are used in someprisons and high security areas in government and industry. However, thepublic perception of intrusiveness has kept such systems from widespreadapplications in everyday transactions. Complexity of the systems andcosts have also slowed development and implementation.

Identity verification by means of written signatures, electronicallyrecorded, has long been known, in spite of significant shortcomings. Oneadvantage of systems using the familiar signature and pen is thatintrusiveness is not considered a problem. The signature is commonplaceand expected in everyday financial transactions and as a means ofgeneral identification. Also, a major advantage of signatures asidentification is the unique role that the signature plays in humanaffairs. The signature of ink on paper has been, and continues to be,the quintessential mark of business. No substitute for the signature islikely to be developed. Contracts, credit card slips, and checks becomelegal, once signed. The requirement of legal signatures on documentsincreasingly causes a bottleneck when the rest of the information anddocumentation is transmitted electronically.

Dynamic signature verification typically records the various pressures,velocities, accelerations, and directions of writing by means oftransducers or accelerometers housed in a special pen or writing plenum.Reference signatures are acquired during an enrollment process. Theelectronic signals from the reference signatures are analyzed and storedfor comparison to offered signatures during a verification transaction.

Dynamic signature verification systems should be distinguished fromsystems designed just to capture a signature and replicate it laterwithout verification. Also, plenum (or pad-based) systems which houseelectronic devices in the writing pad rather than the pen itself shouldbe distinguished. The system described herein consists of a stylus (pen)containing pressure sensing transducers, a unit for amplifying,digitizing, sampling, storing, and transmitting these signals via phone.Finally, algorithms are developed for the analysis of the specific andunique type of signals sent by the data input stylus. Special algorithmsare developed for the processing of signal trains from signatures forenrollment of reference signatures and for enrollment of the digits 0-9,and for later verification of identity of persons, date, and content ofelectronic messages.

Digitized signatures alone do not solve all of the problems relating toauthenticity of documents transmitted or preserved in an electronicmedia.

Traditionally, documents preserved on paper and deemed to be importantare printed or typed with no room for additions later, signed in ink bythose involved, and the date is written after the signature in ink. Inaddition, the document might be witnessed and signed by another partyand/or stamped with a dated seal of a notary. These are the routinesafeguards in place at present for important documents preserved onpaper.

The digitization of data, while presenting new opportunities for rapidtransmission and easy storage, also presents some new problems. Even ifaccompanied by a digitized signature, the integrity of the electronictransmission of a signed document may not be preserved to the level ofthe paper standard of protection. For example, at least for electronictransmission of a signed document, three possibilities for deceptionexist:

1. The digitized signature might be recorded and played back in lieu ofthe pen generated signature for forgery purposes.

2. The text of the electronic document might be modified above thesignature without apparent tempering.

3. The date of an electronic document could be changed at will,electronically. These types of problems have been dealt with extensivelyby researchers at Stanford University and MIT using a 2 keycryptosystem—individuals having a “private key” and “public key” toinsure the integrity of electronic messages. The National Institute ofStandards and Technology is also working along similar lines to developa digital-signature standard based on the public-key system. Keyencryption systems, however, attempt to produce a non-biometric “digitalsignature” which is fundamentally different from the digitized biometricelectronic signature described herein.

PRIOR ART

Known in the art of dynamic signature verification are a variety of pens(styli) containing electronic sensing means designed to measure somecombination of dynamics such as pressure, acceleration, velocity, ordirection produced while signing a signature.

U.S. Pat. No. 3,528,295 issued Sep. 15, 1970 to Johnson et al., is anearly version of a data input stylus. Disclosed is a pen containingpressure responsive transducers mounted therein. In the first,relatively simple embodiment of the stylus, a single transducer isprovided for measuring downward (z-axis) pressure.

In a more sophisticated embodiment of U.S. Pat. No. 3,528,295 fouradditional transducers are provided which are oriented in an orthogonalrelationship to provide information in two additional axis (x and ydirections). During writing signals would then be generatedcorresponding to the pressures exerted in the left to right directionson the plane, or paper (x-axis), far to near (y-axis), and downward(z-axis, sometimes called “p” for pressure downward).

Subsequent work continued to rely on the three axis model usingvarieties of dynamics along one, two, or all three axis.

Obtaining unambiguous readings on the x-y plane (that is, distinguishingx signals from y signals on the plane) was problematic since it requiredthat the pen be held in the same way and not rotated in the hand betweensignatures.

U.S. Pat. No. 3,906,444 issued Sep. 16, 1975 to Crane et al.,demonstrates a pen shaped in such a way as to be held in only onecorrect way when signing. The output signals represent the directionthat the pen is moved, which is converted into direction per unit oftime.

U.S. Pat. No. 3,986,403 issued Oct. 19, 1976 to Hurd et al., measurespressures along the x, y, and z (also called “p” for pressure) axisusing a number of strain gages. This pen is also designed to be held ina particular way.

U.S. Pat. No. 4,078,226 issued Mar. 7, 1978 to EerNisse et al., measurespressure forces proportional to the acceleration of the writing tip(muscle movements) distinguishing x and y forces. In one embodiment apressure sensitive writing surface utilizing piezoelectric transducersis provided to produce an output representing the z (pressure downward)force.

U.S. Pat. No. 4,513,437 issued Apr. 23, 1985 to Chainer et al., isdesigned to measure acceleration along the x,y axis. That is, theorthogonal forces lying essentially in a plane perpendicular to the penaxis. The remaining axis, z (or pressure) is measured with a pressuretransducer.

U.S. Pat. No. 4,896,543 issued Jan. 30, 1990 to Guliman discloses athree-axis force measurement stylus designed to generate an electricalsignal representing the force applied in the direction of motion takenin writing. Strain gages are used to sense force in three dimensions(along three axis).

U.S. Pat. No. 5,111,004 issued May 5, 1992 to Gullman contains a seriesof sensor portions in a PZT annulus which is designed measure anddistinguish pressure applied along the three distinct axis, x, y, and z.

Also known in the art are a number of methods of analysis or algorithmsdesigned to analyze the incomning signals of a data input stylus todetermine if the sample signature under consideration matches thereference signature data on file.

U.S. Pat. No. 3,983,535 issued Sep. 28, 1976 to Herbst et al., also hasas a preferred embodiment input device a tablet, or plenum, which allowsunambiguous x ) and y signals on a plane. This method is based on thetheory that accelerations of the stylus, which are proportional to themuscle forces exerted by the signer, are of predetermined consistentdurations when forming particular strokes. The nature of the processgives rise to various distortions in the time axis: e.g. pauses betweensections of the name, skipped strokes, decorative rubrics, etc. Thus thesignal is marked by regions of high correlation of unknown durationseparated by variable regions of low correlation. Accordingly, theinvention deals with a method of regional correlation which attempts toregister these regions, at first based on stylus contact (segmentation),shift them individually to find the maximal of a correlation function.

U.S. Pat. No. 4,128,829 issued Dec. 5, 1978 also to Herbst et al. is animprovement of U.S. Pat. No. 3,983,535. While U.S. Pat. No. 3,983,535was based on a single acceleration parameter of the signature dynamic,U.S. Pat. No. 4,128,829 uses two orthogonally disclosed (x and y axis)acceleration components along with pressure patterns (z axis).

The x, y, and z components must be processed in complex format andcombined to form a complex correlation wherein the correlation magnitudeis utilized for subsequent decision purposes.

The pen required would have x and y accelerometers along with theability to measure the pressure signal with some sort of axially mountedpressure sensitive transducer mounted in the pen. The preferred penwould need to be un-oriented (not shaped to it was required to be heldin a particular way to orient the accelerometers). Thus the analysissystem is required to mathematically rotate the signals produced inorder to obtain unambiguous x and y data.

U.S. Pat. No. 4,128,829 by Herbst requires a large amount of highlyspecialized and complex hardware. The operation of U.S. Pat. No.4,128,829 must utilize an overall segmentation and relative shiftingscheme as taught in Herbst U.S. Pat. No. 3,983,535. The system alsorequires pens having consistent characteristics for measurement.Finally, the criteria cut-off levels for accept or reject are based onempirical statistical results partially based on large populationtesting bases.

U.S. Pat. No. 4,553,258 issued Nov. 12, 1985 to Chainer et al., usesacceleration and pressure signals but is reliant on segmentation ofsignal trains based on pen-up and pen-down times.

U.S. Pat. No. 4,736,445 issued Apr. 5, 1988 by Gunderson et al., is asignature verification system utilizing a pen input device described inU.S. Pat. No. 4,513,437 which uses bimorph piezoelectric transducerswhich produce electrical signals in response to the rate of change ofaxial pressure on the pen and acceleration of the pen. This patentretains work done in U.S. Pat. No. 4,128,829, mentioned above, regardingthe necessity of segmentation based on pen lifts and correlationscalculations.

The similarity measure developed to accept or reject signatures uses aset of parameters that depend upon the normalized distributions of theinput measures for a general population of users. And prior methods haverelied upon existing data input styli or devices, limiting innovation.

Problems can be summarized as follows:

1. Signature verification systems begin at a data pickup point, either astylus or a pressure pad. The requirement of distinguishing the “x”direction on the plane from the “y” direction causes a number ofproblems. One solution is to employ a pad as a pickup device so the “x”and “y” coordinates are more clearly separated.

In the development of data input pens an early requirement was that thepen be held in a particular way so as not to confuse the “x” and “y”measurements. Later, “mathematical rotation” of the data was substitutedfor the rotation of the pen, but the problems of complexity remained.

In order to make the precise differentiations required, the pensdeveloped tended to be composed of delicate and sensitive parts, noteasily calibrated, that were quite expensive. Making the pen durable andsensitive has been a problem.

2. The data produced by prior art data input pens (styli) is complex andhas no clear analogy to a measured phenomenon. Often, populationparameters are included in an attempt to bring logic to complex dataresulting from the variation of signals coming in from three dimensions(x, y, and z).

The complexity is compounded when additional calculations are used toconvert speed into acceleration measures, or when absolute measures areemployed.

3. Prior art signature verification analysis relies on the segmentationof the signature into signal parts based on pen lifts and pen-down timeson the paper. Such segments are natural, but their variation fromsignature to signature of the same signer causes extreme complexity inallowing for, and correcting, such segment variation.

4. The accuracy of prior art systems is a problem. False rejections,based on a true signer being rejected for variations are not only mostcommon, but provide most of the problems in practice. The algorithmsdeveloped are not easily tuned to the individual registrant and noteasily changed to meet changing conditions.

5. The measurements taken in prior art with the stylus create complexproblems of calibration, requiring sensitive electronic parts tofunction perfectly and be physically adjusted when subjected to changingconditions or abuse.

OBJECTS AND ADVANTAGES

The disadvantages and obstacles in the prior art are overcome in theinvention disclosed herein, by taking advantage of a fundamentallydifferent stylus (data input pen) device. The data collection deviceallows the verification data to be collected and treated infundamentally new ways in signature verification enrollment andverification algorithms.

Accordingly, several objects and advantages of my invention are:

First, that a fundamentally different stylus is disclosed that measuresa new signature dynamic called the relative angle.

Measurements are made of the variations around the relative angle of thesigner. To measure the relative angle and the resulting variationsaround the angle, a new stylus design is incorporated with the followingadvantages,

a. The orientation of the pen on the writers hand (the rotation of thepen) and the direction that the pen moves in an x-y plane in relation tothe paper writing surface, is irrelevant to the measurements taken.Thus, the pen need not be shaped in a particular way nor themeasurements manipulated or mathematically rotated later.

b. The measurements taken are simpler than those measured on a threeaxis model since the x and y axis are not differentiated, and only aratio is needed to calculate the relative angle.

c. The resulting pen is more durable and less sensitive than thoseutilizing delicate electronic equipment. The measurements derived arerelative to one another and absolute accuracy is not required to asgreat a degree.

d. The resulting stylus is less expensive and more durable since justtwo simple transducers are used to arrive at a ratio measurement.

e. Calibration is not necessary, nor any fine adjustments to componentsof the stylus. Rather, calibration is simplified because of the basicnature of the two forces measured. Calibration is ongoing and achievedby a measurement step rather than alteration of the physical apparatustaking the measurements.

A further fundamental difference and advantage is that the resultingmeasurements taken allow a simplified and more useful enrollment andverification method (algorithm). The disclosed algorithms have thefollowing advantages:

a. The measurements taken are based on a concrete analogy to thephysical reality of dynamic signature measurement. The relative angle is“like” the actual angle of the pen in relation to the surface of thepaper. The simple ratio of direct pressure to lateral pressure on thestylus is the measurement definition of relative angle. This analogyallows for data reduction which is necessary for simplicity. Also,complex correlations without analogy are avoided as a method ofverification.

b. The disclosed enrollment algorithm is more easily fine-tuned to theparameters of the individual signature. This allows more accuracy andthe reduction of Type I (false rejection) and Type II errors (falseacceptance) in verification. Also, there is no reliance on populationparameters of signatures so probability plays a lesser role inverification.

c. The analysis of the data in the algorithms does not use segmentsbased on pen-up and pen-down times. Segments used are simple divisionsof the signal train which relativizes the duration of the signals andprovides simple measurement points.

d. The increasingly higher calculation speeds of computers is takenadvantage of to measure large numbers of measurement points based on therelative angle of a signature. The selection of just the most consistentfrom these large numbers tailors the enrollment to the true signer, andallows continual simple adjustments to be made to the signaturediscriminate measures.

e. Calibration is achieved continually as the stylus is replaced in theholder and thus subjected to a standardized downward force. Modificationto direct pressure readings, and lateral pressure readings are doneautomatically and electronically without adjusting the stylus.

f. Verification time is greatly reduced once enrollment is establishedsince the algorithm examines only at assigned measurement points fromthe flood of incoming data.

g. The signature discriminates resulting are not extremely complexcorrelations, but rather highly individualized simple measures derivedfrom the relative angle measures.

h. The verification criterion are easily updated to reflect changes inthe way a signature is signed over time. Also, the signature stringencyscores, the score of matched points that must be attained forverification, can be easily adjusted to meet a variety of changingconditions.

i. During the enrollment for the signature verification system, theenrollee is asked to sign (write) the name of each month of the year andthe ten digits “0,1,2,3,4,5,6,7,8,9.” Thus, when the signer dates thedocument, the digitized true signature for that signer is differentevery day. The digitized signature cannot be recorded and played back insuch a way as to mimic the true signer's signature and a date stamp isthus automatically attached to the document.

j. The text of a document can be reduced to a summary number in such away that any alteration of the text during electronic transmission orstorage would change the number. An enrolled signer could then not onlytransmit a true signature, but also a number, verified as being derivedfrom the writer, which guarantees unaltered text accompanying thesignature, the number transmitted, being independently calculated by thereceiver of the message.

DRAWING FIGURES

In the drawings, closely related figures have the same number butdifferent alphabetic suffixes.

FIG. 1 shows vector forces measured in prior art.

FIG. 2 shows the direct and lateral pressures and their relationship asa relative angle in the present invention.

FIG. 3 shows the pressure sensitive data input stylus.

FIG. 4 shows a signal processing unit diagram.

FIGS. 5A and 5B show a flow-chart indicating a computer algorithm forthe signature enrollment process.

FIG. 6 is a flow-chart indicating a computer algorithm for the signatureverification process.

FIG. 7 is a hypothetical chart of a signature using relative angle asthe measurement method.

FIG. 8 is an alternative embodiment of the invention showing a SVS deskunit providing stylus calibration.

FIG. 9 is a step diagram describing operation of the SVS desk unit shownin FIG. 8.

FIG. 10 is a step diagram describing how the SVS system summarizesdocuments as digits and provides document authentication.

REFERENCE NUMERALS IN DRAWINGS

30 Stylus vector diagram

32 Downward force of handwriting

34 Pressure relay tip

36 Direct pressure vector

38 Lateral pressure vector

40 Relative angle

42 Electrical lead wires

50 Data input stylus

52 Stylus writing tip

54 Stylus tip opening

56 Stylus nose piece

58 Lateral pressure transducer

60 Stylus cartridge

62 Retainer ring

63 Plunger stop ring

64 Direct pressure plunger piece

66 Direct pressure transducer

68 Retainer plug

70 Stylus housing

72 Empty section of stylus

74 Transducer transmission wires

76 Stylus transmission tether wires

78 Vector force diagram

90 Direct pressure signal train input

92 Lateral pressure signal train input

94 Direct pressure amplification

96 Lateral pressure amplification

98 Power pack

100 Analog/Digital converter (sampler)

102 Computer memory

104 Microprocessor/sequencer

105 Computer storage

106 Modem

108 Microcomputer

110 Phone transmission link

130 Signal processing for enrollment

132 Begin enrollment (signal from central)

134 Signal trains received at central computer

136 “D” and “L” amplitude recorded

138 Ratio of “D” and “L” at each sample point

140 Define signal train segments

142 Calculate relative angle of segments and whole

144 Compare relative angle of segments (measurement points)

146 Calculate difference in relative angle of segments

148 Repeat above procedures for all signal trains

150 List measurement point values from all signal trains

152 Calculate range of values at each measurement point

154 Select least-range measurement points

156 Tentative measurement point discriminate selection

158 Test tentative measurement points

160 Adjust discriminates if necessary

162 Assign discriminates

164 End enrollment process

180 Verification signal processing

182 Extract measurement point values from signal train

184 Compare reference measurement point values to sample signaturemeasurement

point values.

186 Add total matches

188 Determine if score is above stringency cutoff

190 Determine if score is below stringency cutoff

192 Send accept message (if above stringency)

194 Send reject message (if below stringency)

210 Relative angle

212 Lateral pressure percentage

214 Direct pressure percentage

216 Quadrant segments

218 Decimated segments

220 Percentage of duration

222 Sample points, relative angle

224 Relative angle average line

226 Sample point variation around average

228 Pen up sample points

240 SVS desk unit

242 Data Input stylus

244 Stylus calibration holder

246 Pressure plate

250-270 operational steps performed by SVS

DESCRIPTION

FIGS. 1 to 10

Before proceeding with the detailed description of the operation of theactual hardware and software of the present invention there will followa brief description of the theoretical basis for the invention and adescription of the forces which the system senses and analyzes.

The method of data collection and method of analysis of the presentsystem is based on my work with actual writing instruments and theforces and pressures present when writing. Unlike prior artconceptualizations of three axis (dimensions) of motion and force indynamic signature analysis, the present system is based on two basicpressures exerted on the stylus while writing. Prior artconceptualizations of the measurements possible with the stylus areindicated in FIG. 1. Prior theories were based on muscle pressuresexerted through the stylus causing variations in downward pressure (zforces), and variations in directions, velocity, or acceleration alongthe x,y axis of the plane.

In contrast, FIG. 2 indicates the forces and resulting pressuresmeasured in a fundamentally different way in the present invention. Thedownward force of handwriting 32 through the stylus 30, caused by handmuscle pressure is, at any given point in time, a simple downward forceabsorbed at pressure relay tip 34. Other writing dynamics may bepresent, such as the direction or acceleration of the stylus, but thesedynamics are not measured in the present invention. At a given moment (adigitized sample point) during a signature the downward force of writingis absorbed by the pen starting at the pressure relay tip 34, in twofundamental and measurable ways. First, there is a direct pressure 36which is the axial, plunger-like force produced in the stylus. Secondly,a lateral pressure 38 is produced because the pen is used at an angle tothe writing surface, and because writing takes place from left to rightmoving the pen along in a lateral direction.

The two basic forces or pressures, added together, equal the totalforce. Importantly, the two forces present are not used as variablesindividually, but rather form a single measure based on their ratio, andthe variation in that ratio. The two pressures, measured by transducers,produce electrical signals relayed for processing and analysis byelectric lead wires 42. Measurements are more static than dynamic, asthe ratio is measured at individual sample points based on thedigitization of the data. These basic measures form the building blocksfor the analysis of the variation of the ratio throughout the signature,and are manipulated to define unique signature discriminates forverification.

The ratio of the two basic pressures can be conceptualized andvisualized as an angle 40 of the stylus to the writing surface. Theratio of lateral pressure 38 to direct pressure 36 indicates the angleof the pen to the surface which is known as the relative angle 40, or“RA”. As the angle of the pen becomes more perpendicular to the writingsurface when pressure is applied, the relative direct pressure increasesand the relative lateral pressure decreases. This relationship of directand lateral pressure is reversed as the pen angle becomes morehorizontal to the writing surface. The two pressures are measured in astylus (FIG. 3) designed to measure the inverse correlation. As in anyratio relationship the actual total pressure and variations in grosspressure is held as a constant. The measurements are indicators ofangle, not necessarily precise measurement of angle, since anglemeasurement, in itself, is not a goal of the invention. Thus, thenotation of the stylus, or the movement of the stylus along thehorizontal plane of the writing surface, is largely irrelevant.

This theory of analysis, based on lateral and direct pressures and thevariations of their ratios during a signature, has an analogy which ishelpful in visualizing the process. The analogy is that of a motionpicture film taken of the hand and pen during the signing of asignature. If a camera took twenty frames per second and the signaturelasted five seconds, the film could be made into one hundred stillphotographs of the signing.

These hundred photographs represent the digitization of the signalcoming from the pen. They are static snapshots in time, like a digitalsample of electronic signals. If the photos were laid out in order, someinformation about the signature would be available and some would not.The photographs would reveal the angle of the pen to the writing surfaceat each point in time, and would reveal the total time as the sum of thephotos. Exact measurement of time and amplitude are only used forconversion to ratio relationships, however. Duration and amplitude areonly finally measured in a relative way for analysis.

The photos provide limited information about the signature. But in thiscase using less information is not a hinderance, but rather, a desiredadvantage. Advanced artificial intelligence computer algorithms make useof the concept of data reduction by analogy. Maximal data collection isnot attempted in favor of useful data collection based on a concreteanalogy. This technique is aided by the increasing speed of computerswhich allow many calculations using the specifically limited data.

Continuing the analogy of the hundred photographs, the stylus angle ineach photo could be measured with a protractor and the angle to thewriting surface noted. When all the photos were so measured the averageangle for the entire signature could be determined. This measure, calledherein the relative angle average, is itself a variable since the sameperson could write at different angles depending on the desk height orother environmental conditions. The critical measurement is not theoverall average relative angle, but the specific and unique variationsaround the relative angle which take place while signing a signature.The particular variations around the overall average relative angle arequantified by examining ratio relationships within in the signature,specifically between segments of the signature signal train. Thesevariations I call measurement point values, which are also relativemeasures, not absolute.

The analysis performed here makes use of a technique known in the art assegmentation. That is, dividing the signature signal trains into partsfor analysis. But segmentation is used here in a fundamentally differentway. Much prior art segmentation has to do with the detection anddefinition of segments occurring as the stylus is lifted off the paperwhen signing, thus creating a series of natural segments of pen-downtimes. This method has caused great amounts of increasing complexitysince signers naturally vary their signatures in ways that could changethe segment count. For example, not dotting an “i” could change theentire segment profile.

Segmentation of signature signal trains is useful for analysis, but itcan be more easily accomplished in the present system by simply dividingthe total signal into ten equal parts. Similarly, additional segmentscan be created by dividing the signal into any number of equal parts.Signal trains can be divided into four equal parts, one hundred equalparts, or twenty five equal parts, and so forth. It will be obvious thatthis method standardizes the duration of the signal, making actualdurations irrelevant. Also, since segment comparisons are used foranalysis, it is apparent that only a small number of segmentations arenecessary to provide large numbers of mathematical combinations ofsegments for analysis.

To perform an analysis, the first signature segment would be comprisedof the first ten percent of the signal if segmentation were done intoten parts. This decimation of a signal 218 is indicated in FIG. 7.Quadratic segments 216 are also indicated in FIG. 7, each segment beingone quarter of the signal. The average relative angle 224 is the averagefor the entire signal and will not, in most instances, be identical toindividual segments. The relative angle of digitized sample points(indicated by the dots in FIG. 7) for the first decimated segment 218will be different than the relative angle of the first quadratic segment216. This difference is caused in part by the high direct pressuredigitized sample points 222 which resulted, in this example, by thedotting of an “i” in a signature. Thus, the first segment would then beexamined to determine the average relative angle of that segment alone.Then a comparison is made between the relative angle of the firstsegment and the relative angle of other segments and the signature as awhole. In addition, many other comparisons are made based on thepossible mathematical combinations. Each specific comparison madedefines a measurement point. Large numbers of measurement points can beextracted by comparing various types of segments to the whole and toeach other (mathematical combinations) and comparing the relative angledifferences, or other statistics (like the range in a segment, orsegment cluster measures) applied to the ratio of the direct to thelateral forces.

In one specification of measurement based on the relative angle ratio(RA), comparisons of one segment to another, and to the whole, are made.A difference measurement is calculated, representative of a variation inthe signal, called a measurement point value. It is critical to notethat the ratio of direct and lateral forces is the electronic indicatorof the angle of the pen, not a precise measurement for the angle. Penangle to paper is the useful analogy for data reduction and analysis.This is important because the overall average relative angle, whileimportant for relative measurements, is not the final measure ofanalysis. Measurement points reflect segment variation around therelative angle irrespective if the relative angle varies from signatureto signature. It is the patterned variations around the average that isthe identifier of signers.

When the stylus is used in a way nearly perpendicular to the surface the“D” or direct pressure predominates. When the pen is slanted greatlyapproaching being parallel with the surface the “L” or lateral pressurepredominates. The two forces taken together always equal the total forceapplied. The relation of these force vectors to the data input stylus ofFIG. 3 is shown in vector force diagram 78. The absolute force downwardis treated as a constant rather than as a variable, as in prior art. Ifthe pen is initially calibrated so that at a 45 degree angle to thesurface a downward pressure on the stylus tip measures fifty percentlateral pressure and fifty percent direct pressure, it will be seen thatthe actual force, no matter how hard or variable, will not affect theessential ratio of the two basic forces. Thus force itself is held as aconstant with only the ratio being measured and indicating the angle.This is a critical distinction between the present methodology andearlier conceptualizations of the “z” force as being a variablereflecting variations in downward pressure to be measured.

In the same way the lateral pressure does not attempt to makedistinctions in direction or acceleration, but is useful only incombination (ratio) with the corresponding direct pressure, combining tocreate the measurements of variation around the average relative anglewhich are the essential measurements of this system.

Thus, the measures that describe individuals by their signature is notsought in population parameters or complex correlations as in the priorart. The unique signature characteristics are determined by theindividual signer as that signer provides a variety of signatures. Theenrollment signatures instruct the enrolle to sign in a variety of ways,such as faster or slower, larger or smaller, and harder and softer, inorder to make the consistent measurement points and measurement pointvalues stand out more clearly in the analysis. Recent increases incomputer speed allow very large numbers of segment comparisons to bemade inexpensively and quickly. Of the large number of measurementpoints examined by the computer, a smaller number will be consistent andrelatively unique for that signer. These areas of consistency providethe simple, relatively invariate, unique measures for signatureverification. The resulting small number of specific measurement points(MPs) that identify an individual are called the signature verificationdiscriminates.

Once the specific discriminates have been identified in the enrollmentprocess, the verification procedure is greatly simplified by extractingonly these values needed for comparison from the incoming signals forcomparisons to the reference standards. Parameters are also easilyadjusted as conditions dictate.

FIG. 3 shows the structure and internal components of data input stylus50. Stylus housing 70 is substantially tubular, housing components whichare substantially cylindrical. Stylus housing 70 has an opening at oneend for the writing tip 52 of stylus cartridge 60, and at he other endfor transducer transmission wires 74 which attach to stylus transmissiontether wires 76. Stylus tether wires 76 and transducer wires 74 supplyelectricity to direct pressure transducer 66 and transmit electricsignals out of data input stylus 50. Stylus tether wires 76 andtransducer wires 74 also supply electricity to lateral pressuretransducer 58 and transmit electric signals out of stylus 50. Stylushousing 70 is composed of metal or durable plastic.

The pressures sensed while writing with data input stylus 50 originatein writing tip 52 as a signature is signed on a writing surface. Thedownward pressure of writing is indicated in vector force diagram 78where “P” is handwriting pressure downward on the writing surface withdata input stylus 50. In response to handwriting pressure two pressuresare measured in the stylus, the lateral, or “L” pressure, and thedirect, or “D” pressure, indicated in vector force diagram 78.

Writing tip 52 is part of the stylus cartridge 60 which is movable inresponse to handwriting pressures. In this embodiment stylus cartridge60 is a ball point pen refill cartridge which is replaceable. Styluscartridge 60 is movable, within a predetermined limited range of motion,in two ways. First, direct pressure is registered through styluscartridge 60, and transferred through direct pressure plunger piece 64,which is also movable axially within a predetermined range. Plungerpiece 64 presses against direct pressure transducer 66 producingelectrical signals proportional to variations in direct, axial pressure.Excessive direct pressure against transducer 66 is prevented by plungerstop ring 63 attached to tubular portion of plunger piece 64. Stop ring63 comes in contact with retainer ring 62 at maximum allowable pressureon transducer 66. Retainer plug 68 is attached to the interior surfaceof stylus housing 70 and holds direct pressure transducer 66 in place.Retainer ring 62 is secured to the interior of stylus housing 70.Plunger piece 64 is held in place by having the disc portion contiguouswith transducer 66 on one side, while the other side is contiguous andheld in place by retainer ring 62. Retainer ring 62 has a center holethrough which passes the tubular portion of the direct pressure plungerpiece 64. The tubular portion of direct pressure plunger piece 64 passesthrough the center hole of retainer ring 62 and secures stylus cartridge60. The tubular portion of plunger piece 64 is of a larger diameter thanstylus cartridge 60 so that limited lateral motion of stylus cartridgeis permitted at the writing tip 52. Stylus cartridge 60 snaps intoplunger piece 64 at the base so that the stylus cartridge will not fallout of stylus housing 70, yet limited lateral movement is permitted.

Writing tip 52 and stylus cartridge 60 are also movable laterally inresponse to handwriting pressures. Lateral pressure is transferredthrough stylus cartridge 60 as sideways pressure against lateralpressure transducer 58. Transducer 58 measures only one force, sideways,irrespective of direction. Transducer 58 is molded to surround styluscartridge 60 but allows sufficient clearance so that the axial movementof stylus cartridge 60 is possible. Another embodiment uses a pressuresensitive pad, attached to the interior of stylus housing 70, wrappedaround interior of stylus housing 70, but not restricting the axialmovement of stylus cartridge 60.

Transducer 58 is secured to the interior surface of stylus housing 70.The exterior surface of stylus cartridge 60, and the interiorcircumference of lateral pressure transducer 58, is composed of a lowfriction material to allow axial movement even when stylus cartridge 60is in contact with lateral pressure transducer 58 when writing.

Nose piece 56 is removable allowing access to the interior of stylushousing 70. The hole in the tip of the nose piece, stylus tip opening54, allows the stylus cartridge to pass through the stylus housing 70.Stylus tip opening 54 is of a predetermined diameter so as to preventexcessive lateral pressure against lateral pressure transducer 58 bylimiting the lateral movement of stylus cartridge 60 to a predeterminedlateral range of motion.

Lateral pressures against lateral pressure transducer 58 by styluscartridge 60 during writing relay electrical signals proportional topressure from lateral pressure transducer 58 through transducertransmission wires 74, through stylus transmission tether wires 76, tosignal processing means.

In a like manner direct pressures against direct pressure transducer 66relays electrical signals proportional to pressure from direct pressuretransducer 66 through transducer wires 74, through stylus tether wires76 to signal processing means.

Empty section 72 of the data input stylus provides room for electronicequipment, as miniaturization progresses, but such equipment is not partof this patent. Another embodiment allows larger transducer means tooccupy the empty section 72.

FIG. 4 diagrams the signal processing unit which receives signals fromthe pressure sensitive data input stylus 50 shown in FIG. 3. Signalsproduced in data input stylus 50 enter the signal processing unit fromdirect pressure signal train input 90, and lateral pressure signal traininput 92. The inputs arrive by way of stylus tether wires 76 of datainput stylus 50 shown in FIG. 3.

In FIG. 4 direct pressure transducer signal trains from stylus arrive atdirect pressure signal input 90 and are amplified by the direct pressureamplifier 94. Lateral pressure transducer signal trains arriving atlateral pressure signal input 92 are amplified by the lateral pressureamplifier 96.

At analog/digital converter 100 both arriving signals are sampled by theprocess of being digitized. Digitized signals are used in the systemfrom this point forward. The digitized signal trains then are processedand operations sequenced by microprocessor/sequencer 104. In thepreferred embodiment the computer memory 102, microprocessor 104, modem106, and computer storage 105 are comprised of a microcomputer 108. Inthis embodiment signal inputs 90 and 92, analog/digital converter 100,and power pack 98 comprise a peripheral device for an existingmicrocomputer 108. In this embodiment the signal processing unit islinked to the central enrollment and verification computer at a distantlocation. The phone transmission link 110 allows sequencer to receiveinstructions from the central computer during enrollment algorithmprocedures (FIGS. 5A-B) and during the verification algorithm procedures(FIG. 6).

The signal processing unit, in this embodiment, receives the stylusthrough an opening for storage of the stylus (see FIG. 8). This “penholder” arrangement also serves the calibration function of theprocessing unit since the stylus is held in a pre-determined position ofknown angle.

In a second embodiment all of the components in FIG. 4 are contained ina signal processing unit. Power pack 98 supplies electricity to allcomponents and is plugged into standard AC current.

Modem 106 sends signal trains to a central verification and analysiscenter via phone transmission 110. But in a second embodiment parametersfor verification are held in storage 105 while analysis of enrollmentsignatures still takes place at a central location via phone 110.

Modem 106 allows signal trains to be sent to a central location andallows accept or reject messages to be sent back to the localverification station where the signal processing unit is located. Thesignal processing unit is also used to collect reference signatures foranalysis and to transmit these signatures to a central analysis centerwhere computer programs (FIG. 5 A-B) are used in the analysis of signaltrains and the establishment of specific electronic signaturediscriminates for individual signers.

FIGS. 5, A-B is a flow chart describing a computer algorithm used as amethod for enrolling reference signatures in a signature verificationsystem. The first step 130 provides signal trains to a central computerlocation originating when an enrolle uses the data input stylus shown inFIG. 3 to provide enrollment signature signals which are processed bymachine method shown in FIG. 4. The data input pen shown in FIG. 3, andthe signal processing device shown in FIG. 4, are used in the system toproduce and transmit reference signatures, written months of the year,and handwritten digits 0-9 as well as signal trains to be verified at alater time. The enrollment process begins in the second step 132 as theprocess is initiated by the central computer and relayed tomicroprocessor 104 of the local signal processor. Electronic signalsarrive via phone for analysis at a central computer 134.

The enrollment procedure requires an enrolle to use the data inputstylus when signing twenty enrollment signatures. An enrollment form,used in the beginning of the enrollment process 132, indicates how thesignatures are to be signed by the enrolle: faster vs. slower, largervs. smaller, harder vs. softer, and the resulting combinations of theabove. These combinations result in requests for signatures signed inthe following ways: fast/hard, fast/large, fast/small, fast/soft,slow/large, slow/small, slow/hard, slow/soft, large/hard, large/soft,small/hard, and small/soft. In addition to these specific signinginstructions, the enrolle is asked on the form to provide eightadditional normal signatures.

In the third step 134 the signals are received and stored at the centralanalysis location. Each signal train, representative of a signature, istreated separately during analysis.

The fourth step 136 records the direct pressure amplitude and thelateral pressure amplitude for each digitized sample point in the signaltrain. Digitization used for sampling involves a sampling rate in therange of 100 samples per second, so an average signature will consist ofapproximately 500-800 sample points and the accompanying values ofdirect and lateral pressure. There is, however, no need for a maximumallowable time to sign an enrollment reference signature.

The fifth step, 138 calculates the ratio of the direct pressure signalamplitude to the lateral pressure signal amplitude at each sample point.This standardizes amplitude as a ratio for further calculations. Theresulting values are known as the relative angle ratios.

When the relative angle ratios have been calculated for all digitizedsample points the analysis shifts to calculations involving the durationof the signal trains and the division of the signal train into parts, orsegments.

The sixth step 140 divides the signal trains into equal part segmentsfor analysis. The signal train is divided into quadrant segments, eachsegment being 25 percent. The same signal is then divided into decimatedsegments, each segment being 10 percent of the signal train. The signaltrain is then divided into twenty five segments, each being 4 percent ofthe signal train. And finally, the signal is divided into 50 parts, eachsegment being 2 percent of the signal train. This process is not limitedto the segment divisions listed, and, if more segments are needed in theanalysis, other kinds of segments can be defined and the signal traindivided in other ways. The resulting segments are defined by the samplepoints and the values of the sample points falling within them.

The sixth step 140, defining segments, converts signal train durationsto relative measures as each complete signal train is considered onehundred percent of the signal train, no matter how long, and thendivided on that basis.

Having defined segments and assigned sample points and their ratiovalues to each segment, various calculations can be made for eachdefined segment. The seventh step 142 averages the amplitude ratios ofsample points within each segment, and averages the ratio points for theentire signal train. This results in each segment having a relativeangle measurement as well as the whole signal train having a relativeangle measurement. The relative angle of the entire signal train mightwell vary between signal trains from the same signer, so the overallrelative angle is not used as a discriminate. However, the relativeangle of the entire signal is useful as the average around which thesegment relative ratios fluctuate. The unique nature of some of thesefluctuations for an individual signer form the basis of the signaturediscriminate measures.

The eighth step 144 compares all segment measurements to each other.Each segment is compared to each other segment in all possiblemathematical combinations. When the signal train has been divided intofour segments, ten segments, twenty five segments, and fifty segments,this results in eighty nine defined segments. There are 3,916 possiblecombinations of two segments, or comparisons, that can be made. Eachcomparison is called a measurement point. The number of measurementpoints needed is a variable depending on computer speed andcomprehensiveness of analysis desired. By adding an additionalsegmentation to the above defined segments of seventy five segments, thetotal number of segments would then be the original eighty nine plusseventy five which equals one hundred and sixty four segments. Thenumber of combinations thus increases to 13,366 combinations, ormeasurement points.

Additional measurement points can also be created by simply combiningnumbers of segments and treating the combination as one new segment. Thenumber of possible combinations, and therefore the number of newmeasurement points, increases greatly when this method is used. There isno practical limit to segment definition and creation.

The ninth step 146, measures comparisons at each measurement point.Since each segment has a relative angle measurement, the difference inrelative angle at a measurement point results in one measurement pointvalue. If one hundred and sixty four defined segments were analyzed, asin the above paragraph, the 13,366 measurement points would have 13,366measurement point values defining the signal train of the signature.

Step ten 148 repeats the above calculations for each of the twentyenrollment signature signal trains. Each signal train is analyzedindividually, but each measurement point is assigned the measurementpoint values from all signals.

The second phase of the analysis of reference signatures is diagramed inFIG. 5-B. The first step 150 of phase two lists all of the measurementpoint values (MPV's) obtained from the reference signatures for eachmeasurement point (MP).

The second step 152 calculates the range of values obtained at eachmeasurement point from the twenty signatures.

The third step 154 selects a smaller number of measurement points havingthe lowest ranges, in this case 500 measurement points, to serve astentative signature verification measurement points.

The fourth step 156 defines the selected low-range measurement pointsand their range of acceptable values. The range of acceptable values issimply the range of scores obtained at a given measurement point duringenrollment. A tentative stringency score consists of the number ofmeasurement point matches a sample signature must achieve to beverified. The tentative stringency score need only be an educated guess,based on other similar ranges of measurement points, prior to testing.

The fifth step 158 consists of testing the tentative measurement pointsand stringency score using actual signatures provided for the purpose bythe enrolle. Here the phone link between the central analysis computerand the local signal processor is again used. A signature signal trainis sent via phone lines to the central analysis center in order to testthe tentative signature discriminates.

The sixth step 160 is to adjust the stringency score and the ranges ofthe measurement points if necessary, to balance the probability of falserejections of the true signer against the probability of falseacceptance of a false signer. The enrolle can have some discretion inthe decision about this balance based on the needs of the enrolle. Infact, a variety of stringency scores can be employed for one signerdepending on the importance of the signature. For example, a lowerstringency score for credit card purchases under one hundred dollars ispossible. Thus the possibility of false rejection is decreased becausethe importance of the transaction is less serious. Extremely importantsignings might have an extremely high stringency score.

The seventh step in the second phase of the enrollment process 162,assigns the chosen measurement points, and their acceptable range ofvalues to the individual enrolle. The chosen values are known as thesignature verification discriminates. A second embodiment allows thesignature verification discriminates now identified, to be relayed backto the storage capacity 105 of the signal processing unit. This allowsthe parameters for verification to be kept at the local level, if thisis desirable in a particular application.

The eighth step 164, ends the enrollment process.

FIG. 6 is a flow chart describing a computer algorithm used as a methodfor signature verification, when enrollment signatures have beenprocessed as shown in FIGS. 5A-B, and are on file.

The first step, 180 consists of a putative signer providing a signaturewith the data input stylus shown in FIG. 3, and the resulting signaltrains amplified, digitized, and transmitted for analysis as shown inFIG. 4

The second step 182 in signature verification involves the distantcentral computer extracting, from an incoming signal train of asignature, only the values of the measurement points previously chosento be signature verification discriminates.

The third step 184 in signature verification compares the extractedmeasurement point values of the putative signature with the allowablerange of values on file as the signature verification discriminates.

The fourth step 186 in signature verification consists of adding thenumber of matches achieved by the incoming signals.

If the number of matching points is at or above the predeterminedstringency cutoff 188, an accept message 192 is sent. If the number ofmatching points is below the predetermined stringency cutoff 190, areject message 194 is sent.

Not shown in FIG. 6 is the possible additional step of setting anotherscore which, being close to the stringency cutoff, allows the putativesigner to try again. This feature could help avoid false rejections ofsigners whose signature tended to change slightly over time. Consistentautomatic fine tuning of signature discriminates is thus easily done asthe system is used for verifications.

Another step not shown in FIG. 6 is the possibility of ongoing signatureverification procedures indicating new measurement points which shouldbecome discriminates, and indicating current discriminates which arebecoming less useful over time.

FIG. 7 is a graphic representation of a hypothetical signature plottedso as to indicate how the signal trains are related and analyzed. Thevertical axis of the chart indicates the angle of the stylus relative tothe writing surface, the relative angle 210. The relative angle isactually measured by the ratio of the direct and lateral pressures, alsoindicated along the vertical axis 212. This chart assumes a data inputstylus of the type described herein calibrated so than downward pressureon the stylus tip when the stylus is at a 45 degree angle to the writingsurface, registers 50 percent direct pressure 214 and 50 percent lateralpressure 212.

It is the ratio of the direct pressure to the lateral pressure which isactually measured and is correlated to an angle degree for clarity.Actual variations in pressure on transducers is eliminated as a variableby measuring only the relationship, that is the ratio, of the twopressures measured.

The horizontal axis of the chart in FIG. 7 indicates the duration of thesignal train. But the final measure used is also standardized so thatthe whole signal train is 100 percent, no matter how long it actuallyis. Thus, actual duration is also eliminated from final calculations infavor of relative measures. This is important since variation induration, as in amplitude occurs in different signatures of the truesigner and is an inadequate discriminate measure.

The total signal train being 100 percent of itself, is then divided intoequal parts called defined segments based on a percentage of the signal.The segments are defined as simple parts of the whole, the whole beingone hundred percent 220. Quadrant segments 216 are made by dividing thesignal train into equal quarter segments of twenty five percent each.Decimated segments 218 are defined by dividing the signal train into tenequal parts of ten percent each. The process of creating definedsegments is not limited to the several indicated in FIG. 7 since thesignal can be divided into 100, 20, 50, or any number of segments foranalysis. In practical terms, only a few segment divisions are necessaryfor analysis since a large number of mathematical combinations resultfrom a relatively small number of comparison units.

The plotted digitized sample points 226 in FIG. 7 represent themeasurement of ratio between the direct force of the signal train andthe lateral force of the signal train. The sum of the plotted points inFIG. 7 represent the digitized signals of a complete signature where thepen was lifted from the paper seven times, leaving eight naturalsegments of pen-down times. The pen-up times 228 are indicated in thechart as lying along the line where direct and lateral pressures areequal, which is the same as the 45 degree measurement. Pen-up timescould also be represented as no signal at all, but this distinction isminor since these natural segments, which play a major role in muchprior art, are eliminated from the analysis in the present system.Rather, segmentation, which is necessary, is achieved by simply dividingthe signal trains into defined segments, being equal parts of the whole.Since the analysis of variation is problematic of any given digitizedpoint in itself, comparisons are made of segments of varying lengths.For example, the first segment of the quadrant segments 216 could becompared to the first decimated segment 218 in terms of the average ofthe plotted points within the segments. It will be seen that the firstquadratic segment will have more points of a higher relative angle thanthe first decimated segment, thus the average, not the total points,will be different.

The comparison of two segments yields a measure of their difference, themeasurement point value. The average of all plotted points in asignature is the relative angle 224 of the whole, which in thishypothetical chart, is 54 degrees, or a 40/60 ratio of direct to lateralforce. The average of the whole is, however, a variable itself, since asigner might hold the stylus in different ways at different times owingto environmental conditions or other factors. Thus, this measure also isstandardized, by examining the measurement point values as they varyaround a given average. The actual measure of the average angle is notused as a discriminate. FIG. 8 is a schematic diagram showing a SVS deskunit 240. The desk unit 240 includes a data input stylus 242 similar todata input stylus 50 shown in FIG. 3. A stylus calibration holder 244holds the data input stylus 242 at a predefined angular position (e.g.,45 degrees) in relation to a pressure plate 246. The SVS desk unit 240is used for calibrating the data input stylus 242 as described below.

FIG. 9 is a flow diagram showing the calibration functions performed bythe SVS desk unit shown in FIG. 8. The data input stylus 242 isinitially inserted into the stylus calibration holder 244,250. Thestylus calibration holder which is typically a piece of formed plasticor metal, subjects the data input stylus 242 to a predetermined angleand pressure in step 252. Held in this predetermined position, andsubjected to a downward force at the tip 53, the readouts fromtransducers 58 and 66 indicate actual direct “D” and lateral “L”pressure in step 254.

The actual direct and later pressures are then recalibrated such that“D” and “L” are equal at the present predetermined angle (45 degreeangle) 256. The stylus can be recalibrated each time the stylus isinserted into the SVS desk unit 240 (FIG. 8). Thus, the signatureverification system is continuously recalibrated for changes in 15transducer operating characteristics or variations between differentdata input stylus operating characteristics.

Referring to FIG. 10, document verification would be preformed in theSVS system as follows:

A given document is captured in an electronic medium in step 258. Thegiven document includes the date and signature of a given signer. Thedocument is processed to determine the number of times a given characteror characters occurred in the document in step 260 (See detaileddescription above).

The SVS system then locates a space position in the document accordingto the number of occurrences of the character(s) in step 262. In step264, the SVS system generates a string of identification digitsaccording to the located space position. A signer writes theidentification digits with the input stylus in step 266. The SVS systemverifies that the identification digits were written by the signeraccording to the relative angle of the data input stylus in step 268.The digitized document and the verification digits are then transmittedto a given transmission location in step 270. The verification digitsare regenerated at the transmission location to verify the originalityof the associated transmitted document.

SUMMARY, RAMIFICATIONS, AND SCOPE

Accordingly, the reader will see that the Signature Verification Systemdisclosed makes possible less expensive, more durable, less complicated,and more reliable signature verification. This is possible because thedata input device and the resulting data analysis is fundamentallydifferent from previous signature verification systems. The simplifiedand more durable stylus along with the simplified and adaptablealgorithm make use in a variety of settings practical. Use is notrestricted to credit card point of sales since the stylus is easilyadaptable to use as a computer peripheral at a remote location allowingaccess by identification in a safer way than code words or numbers.

The algorithm disclosed for use with the simplified and unique stylusalso has a number of advantages allowing widespread applications:

1. The calculations required are simple and fast.

2. The enrollment takes advantage of individual variations, rather thantreating this as a problem.

3. After enrollment, verification is exceptionally fast and accurate.

4. Stringency requirements are easily adjusted to conditions.

5. Resulting signals do not need manipulation based on how the userholds the pen.

6. Verification is not dependent on consistent signing.

Another aspect of the invention further ensures the authenticity ofelectronically captured documents. During the enrollment for thesignature verification system, the enrollee is asked to sign (write) thename of each month of the year and the ten digits “0,1,2,3,4,5,6,7,8,9.”Thus, when the signer dates the document, the digitized true signaturefor the signer is different every day. Therefore, the digitizedsignature cannot be recorded and played back in such a way as to mimicthe true signer's signature.

Given the “enrollment” of months and digits, the standard for a truesignature changes daily. The digital composition of the signaturefollowed by “June 21, 1993” , is a different digital pattern than thesame signature followed by “June 22, 1992” written out with thesignature identification stylus. Not only is the date verified (becausethe date sets the digital standard at the verification center each day)but the digital pattern to be matched by a forgery also changes daily.

During any given day, however, the digitized signature recordedverbatim, could be used for forgeries that day. This problem is avoidedby programming the verification algorithm to reject “exact” copies of adigitized signature since the true signer will sign within the errorparameter but, rarely if ever, sign the exact digital signature. Simplerecordings are simply detectable, and since they could only be used forone day, making sophisticated adjusted recordings for forgeries unlikelyand difficult.

Also, the registration process determines the variation expected indifferent signings by the same enrollee. Therefore, a further safeguardfor important transactions requires the signer to sign twice. Recordedplayback forgery attempts would not indicate the expected variation andwould be detected as forgeries.

Thus, signing the document with the verification stylus, dating thedocument with the same stylus, and writing the multiple digit numberwhich indicates the content of the document with the stylus, linkselectronically the verified signer, the verified date, and the verifiedcontent of the message.

Since the enrolled signer has enrolled the digitized numerals 0 through9, any summary number written along with the signature can be verifiedas coming from the true signer. Given this, one only needs themethodology to derive a summary number describing a document in such away that any variation in the text would change the summary number.

One example of such a simple system follows:

A given document is capture in step 258. In the given document eachletter of the alphabet occurs a given number of times and everyavailable space in the entire document contains one of these letters, isblank, or contains a punctuation mark. Each space (byte) can besequentially numbered in a document.

The following procedure could be carried out for a documentelectronically in a very short period of time—for each letter of thealphabet (or for just vowels), the following steps are taken:

For the letter “A”:

1. The total number of times the letter “a” occurs in the document iscalculated.

(Xa)-(say 89)(meaning the letter “a” occurs 89 times in the document).

2. The space position of the “A” that is the midpoint of all As iscalculated (Xmid)=(say space 3,987) in the document (or the first of 2mid-spaces in even numbers).

3. To summarize, (Xmid) is divided by (Xa)-(44.797753)-to 6 decimalplaces to yield an 8 digit number. The number “44797753” thus is asummary representation of the relationship of the letter “A” to thedocument.

4. This yields an 8-digit number summarizing the relationship of oneletter to the document. (Note: this number can easily contain more orfewer digits—it needs to be long enough to detect changes to thedocument as a whole.)

5. This is done for as many letters as desired (perhaps all 26).

6. All of the 8-digit numbers derived from all letters are added and theaverage taken. This average number summarizes the document as a wholeand when written with the pen system described herein is the basis forauthenticating the content of a particular document.

Thus, a document sent electronically can be guaranteed as to signer,content, and date, with the simple transmission of digitized pen strokesto the verification center. At the end of the electronic document, thefollowing spaces would be provided with the signature identificationsystem described above.

(SAMPLE SIGNING AREA FOR ELECTRONIC DOCUMENT) Signature Date (write outmonth) Doc. ID#

The following is an example of how the signature verification system canbe implemented. A bank customer establishes an account at a local bank.The customer has registered his/her signature using the signatureverification pen and enrollment process described above. Anothercustomer at the same bank or at another bank obtains an “EDO”(electronic deposit only) account number. The EDO number indicates thebank and the account number of the client. The EDO number can only beused to deposit money in a specified account. Thus, the EDO number canbe published to the world, similar to a phone number. The EDO number canbe published on a client's home page and if anyone uses a people finderprogram, the EDO number is published with the client e-mail address.

Persons offering a service or product for sale on the internet, or WorldWide Web (WWW), indicate their EDO number for payment purposes. A buyerwishing to purchase a service or product from the home page (electroniccatalog) connects with his bank where he has registered with the SVSdescribed above. Having been verified, he instructs his bank toelectronically transfer funds from his account to the EDO of the seller.This bank-to-bank transaction completes the payment and the seller isfree to supply the service or product by mail or computer.

For microtransactions, bank can, to a large extent, automate thisprocess. Parameters on amounts transferred and numbers of transactionsare set by the customer. Fraud is reduced dramatically since the onlyincoming transfer of value goes to a known EDO account in a bank fromanother bank.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. For example, the pressure sensitive transducerscontained in the stylus might consist of pressure sensitive film,pressure sensitive resistors, or any number of pressure sensitivedevices small enough for the purpose. Similarly, the enrollmentalgorithm might make use of a variety of standard statisticalmeasurements applied to the developed measures of relative angle inorder to derive additional measurement points. Also, the device mightalso be useful in a variety of settings where personal identification isuseful such as providing a legal signature transmitted electronically,or serving as the identification means for access to restricted areas.

Thus, the scope of this invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

Having described and illustrated the principles of the invention in apreferred embodiment thereof, it should be apparent that the inventioncan be modified in arrangement and detail without departing from suchprinciples. I claim all modifications and variation coming within thespirit and scope of the following claims.

What is claimed is:
 1. A method for digitally summarizing anelectronically captured document, comprising: determining how many timesa given character occurs in the document; locating positions of thegiven character in the document and determining an identification numberthat represents a space position in the document and varies according tothe located positions and the number of times the given character occursin the document; generating a string of identification digitsidentifying the electronic document according to the space position andtotal count of a selected number of characters.
 2. A method according toclaim 1 wherein generating the identification number includes thefollowing: determining a mid-point in the document for the locatedcharacter positions in the document and determining the identificationnumber according to the mid-point.
 3. A method according to claim 2including locating multiple mid-points, a mid-point being the medianlocation of a particular alphabetic character in the document; andderiving the document identification number by combining the mid-pointsfor different characters together.
 4. A method according to claim 1including: writing the identification digits using a data input stylus;verifying that a given signer wrote the identification digits accordingto changes in relative angle of the data input stylus; and independentlyregenerating the identification digits for authenticating the electronicdocument.
 5. A method according to claim 1 including writing a set ofdate verification digits with a data input stylus representing the date;and verifying the signature according to both the date verificationdigits and the generated relative angle values of the signature.
 6. Amethod according to claim 1 including verifying a signature captured inthe electronic document with a signature verification system (SVS),comprising: inputting enrollment data into the SVS, the enrollment dataincluding an enrollment signature, enrollment names for months of theyear and enrollment numerical digits (0-9); storing the enrollment datain the electronic document; capturing a signature of a signer and thedate with the verification system; and comparing the signature and thatdate with the stored enrollment data for verifying the source and timeof the signature captured by the SVS.
 7. A method according to claim 6including the following steps: capturing a second signature of thesigner with the SVS; and determining a set of signature verificationdiscriminates between the two signatures of the signer, the signatureverification discriminates representing a natural variation in therelative angles of the data input stylus each time the signer signs asignature.
 8. A method according to claim 6 including rejecting acaptured signature that is identical with the stored enrollment data. 9.A method according to claim 6 wherein the captured signature is comparedto the enrollment data according to a set of measurement points derivedfrom both the captured signature and enrollment data using a data inputstylus, the measurement points for both the captured signature andenrollment data generated according to the following steps: generating afirst electrical signal having a value that varies according to a directpressure exerted upon a data input stylus in a direction co-axial withthe given stylus axis; generating a second electrical signal having avalue that varies according to a lateral pressure exerted on the datainput stylus in a direction transverse to the given stylus axis, thevalue of the second electrical signal being generated independently ofthe value of the first electrical signal; generating the relative anglevalues according to the values of the first and second electricalsignals, the relative angle value being the ratio of direct to lateralpressure, the ratio of the direct “D” force to the lateral “L” force inthe signal train, at any given time being independent of the actualpressure, direction, or physical angle of the stylus; segmenting thesignal and determining the average D/L ratio in a series of segments;and matching comparisons of segments which produce measurement points,some of which are unique to a specific signer.
 10. A method according toclaim 9 wherein the first and second electrical signal values representa signal train that corresponds with variations in both the directpressure and lateral pressure, respectively, while signing a signatureand including the following steps: segmenting the signal train of thesignature into multiple segments, the multiple segments offered forverification of the signature; comparing the segmented signal train topre-determined relational characteristics for preselected segments ofthe signal train to each other and to the whole signal train; andidentifying similarities between enrollment data to validate the signaltrain as originating from a particular signer.
 11. A method according toclaim 10 wherein a date is written in addition to the signature so thatthe signal train changes daily, the daily varying signal train providinga daily varying data source for comparing with the enrollment data. 12.A method according to claim 11 including the following steps: segmentingthe input signal train from the signature, the written date, anddocument identification digits of the signal train into multiplesegments each representing a portion of one of the signal trainsgenerated by he data input stylus; generating measurement points bycomparing the direct force to lateral force ratio of multiple segmentsto each other and to the average relative angle of the whole signaltrain; designating measurement points as identification discriminatesbased on their relatively low range of variation; and verifying thesignal train based on a predefined range in which a measurement pointresides and the number of measurement points that match.
 13. A methodfor signature verification according to claim 6, including: issuing anelectronic deposit only account number allowing only deposits into theaccount associated with the deposit only account number; electronicallyaccessing a customer bank account to initiate an electronic transfer tothe electronic deposit only account; signing a customer signature usingthe SVS system to verify access authorization to the customer bankaccount; and automatically transferring a customer selected amount tothe electronic deposit only account number if the customer signature isauthorized by the SVS system.
 14. A method according to claim 1 whereina summary number is generated by submitting one particular character ina document to a summarization based on the locations and count of thatparticular character.
 15. A method according to claim 14 includinggenerating multiple summary numbers to further summarizing the summarynumbers thereby summarizing the document with a single number.
 16. Amethod for verifying a signature captured in an electronic medium with asignature verification system (SVS), comprising: inputting enrollmentdata into the SVS, the enrollment data including an enrollmentsignature, enrollment names for months of the year and enrollmentnumerical digits (0-9); storing the enrollment data in the electronicmedium; capturing a signature of a signer and the date with theverification system; comparing the signature and that date with thestored enrollment data for verifying the source and time of thesignature captured by the SVS; issuing an electronic deposit onlyaccount number to a bank client allowing only deposits into the accountassociated with the deposit only account number; electronicallyaccessing a customer bank account to initiate an electronic transfer tothe electronic deposit only account; signing a customer signature usingthe SVS system to verify access authorization to the customer bankaccount; and transferring a customer selected amount to the deposit onlyaccount associated with the electronic deposit only account number ifthe customer signature is authorized by the SVS system.
 17. A methodaccording to claim 16 wherein the captured signature is compared to theenrollment data according to a set of measurement points derived fromboth the captured signature and enrollment data using a data inputstylus, the measurement points for both the captured signature andenrollment data generated according to the following steps: generating afirst electrical signal having a value that varies according to a directpressure exerted upon a data input stylus in a direction co-axial withthe given stylus axis; generating a second electrical signal having avalue that varies according to a lateral pressure exerted on the datainput stylus in a direction transverse to the given stylus axis, thevalue of the second electrical signal being generated independently ofthe value of the first electrical signal; generating the relative anglevalues according to the values of the first and second electricalsignals, the relative angle value being the ratio of direct to lateralpressure, the ratio of the direct “D” force to the lateral “L” force inthe signal train, at any given time being independent of the actualpressure, direction, or physical angle of the stylus; segmenting thesignal and determining the average D/L ratio in a series of segments;and matching comparisons of segments which produce measurement points,some of which are unique to a specific signer.
 18. A method according toclaim 17 wherein the first and second electrical signal values representa signal train that corresponds with variations in both the directpressure and lateral pressure, respectively, while signing a signatureand including the following steps: segmenting the signal train of thesignature into multiple segments, the multiple segments offered forverification of the signature; comparing the segmented signal train topre-determined relational characteristics for preselected segments ofthe signal train to each other and to the whole signal train; andidentifying similarities between enrollment data to validate the signaltrain as originating from a particular signer.